Ok everyone. I have a reoccurring issue with my TPS sensor or something else if someone can help me find out what it is.

I have a 1.6 8v engine and the motor always misfired at 3000 to 3200 rpm when under partial throttle when I got it. After testing the original TPS I found that it had a dead spot in the carbon strip and I assumed that was the issue.

However two new aftermarket TPS later it still has the same problem with the misfire at 3000 to 3200 rpm. The misfire is caused by running full rich and I can see it on my wideband O2 sensor. It hits 9.2 to 10.2 when that misfire happens.

Funny part is if the TPS is completely disconnected mechanically and electrically the problem is non existent. I just get a slight hesitation as soon as I touch the throttle.

If I have it mechanically disconnected from the throttle body and still plugged in electrically the slight hesitation with the throttle goes away and it runs fine at 3000 to 3200 rpm.

Its is like the TPS or ecu does not like that signal as it revs up.

I would like to get this resolved.

The Two new TPS sensors pass two out of three tests on Fixkick.com tutorial. The idle circuit should start off somewhere between 0 to 50 ohms and hit 500 before infinity. Both new units form summit racing (TH147) read 320 ohms starting and as I turn them they hit about 400 ohms drop down to 200 ohms then hit infinity.

I guess they are just crappy parts.....

The fixed resistor ohms are in spec and so is the other test for the full sweep ohms test. No holes like my original. At least from what I can tell with my fluke digital meter.

I would apricate some suggestions.

I got myself on the Fixkick forum and found some good help. I will post back up once I find out my problem.

Have you tried graphing the output of the TPS, the engine doesn't need to be running for this, what you're looking for is to see a smooth change in resistance with no spikes or drop outs.  Your new aftermarket TPS sound like they are defective to me, as I am not expecting to see the resistance go up, then down, then up and finally open circuit - I'm expecting low resistance to higher resistance in a fairly linear fashion - the actual values can be determined from the manuals, but are not critical to this discussion, the smooth progression is what I concerned about.

Take fixkick with a pinch of salt and go to Ack's FAQ and download the factory manuals for yourself.

The TPS is not really a factor in mixture setting, it's primary role is so the ECU can detect when the throttle is closed, wide open, and the rate at which it is opening - if you're familiar with carburetors, the rate of opening correlates to the action of the accelerator pump on a carb, and that is the cause of the flat spot or hesitation when it's disconnected.

I've attached two pdf files for you to look at, these are from the 1.6, 8V Vitara FSM and show the 4 wire TPS sensor, your vehicle may or may not have the same TPS - the first pdf shows a linear graph for the change in voltage as the throttle is opened, this would require a linear change in resistance which, based on your posts, you are not getting with the aftermarket TPS sensors you have.

Fordem,

Thank you for the info. It still could be a tps issue because I recalibrated my settings on it and my misfires occur at a lower rpm now around 2800 to 2900 rpm.

But after unplugging each sensor input to the ecu I found that the temp sensor when unplugged makes the issue go away and it drives quite well.

I tested the ohms range on the sensor and its doing exactly what it needs to. 2800 ohms cold and 300 hot and good in-between.

This morning I also drove the car while it was cold and it performed perfectly but once it got a little heat into it the constant misfire at 2900 rpm comes back.

I am not really sure what it could be.

I will replace the engine temp sensor but I have my doubts if that is the real issue....

You ever deal with something like that before?

Unplugging the sensors is not a particularly reliable way of testing anything - it creates a "hard fault", so the ECU sets a fault code and then attempts to compensate by using a default set of values, so that you are not left stranded on the side of the road - it also turns the CEL on to let you know that you need to have the engine checked.  Because the engine runs well on the default values, unplugging a sensor can mask a problem with a different sensor, making things very confusing.

Unplugging the coolant temperature sensor will prevent the ECU from sensing the engine temperature, and one of the possibilities is that it may not attempt to run in what is called closed loop, which is when the ECU uses feedback from the O2 sensor to set the fuelling - the experience you report with the vehicle running well until it started to warm up strongly suggests that is an open loop/closed loop phenomenon, as the ECU will normally run the engine in open loop until it warms up and then switch to closed loop to reduce fuel consumption & emissions.

If I were in your shoes I would be looking for a genuine TPS sensor - they may be available from places such as megazip.net or partsouq.com - if you give the VIN I may be able to lookup the part number.

Fordem,

Hey buddy. thanks for the info. But I just found the issue with my TPS. Buried under the dash I found that the previous owner that did the swap actually flipflopped one of my TPS wires. The Gray and yellow stripe one. He connected it with the green and yellow wire of the EGR solenoid for some reason. I wired them back to factory settings and she is driving like a champ now.  My timing is working now and feels really strong.

Thanks again for all the help.